Substrate cutting device and method

ABSTRACT

An automatic cutting device is described for cutting an assembly. The assembly includes a material having a weakened zone therein that defines a useful layer and being attached to a source substrate. The cutting device includes a cutting mechanism and a holding and positioning mechanism operatively associated with the cutting mechanism. The holding and positioning mechanism positions the material so that the cutting mechanism detaches the layer from the source substrate along the weakened zone. The cutting device also includes a control mechanism for adjusting at least two different portions of the assembly during detachment of the layer to facilitate a more precise detachment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International application no.PCT/FR03/00002 filed Jan. 2, 2003, the entire contents of which areexpressly incorporated herein by reference thereto.

BACKGROUND ART

The present invention generally relates to the processing of materials,and more specifically processing substrates for electronics, optics oroptoelectronics. In particular, the invention relates to ahigh-precision automatic cutting device for cutting an assembly thatincludes a layer of material having a weakened zone which is attached toa source substrate. The device includes cutting means and holding means.

The invention also relates to a high-precision automatic cutting method,wherein an assembly that includes a layer of material attached to asource substrate is detached via a weakened zone. The method includesholding the assembly with a holding means, and cutting the assembly todetach the layer from the source substrate with a cutting means. Itshould be noted that the invention is particularly suitable for cuttinglayers having a thickness less than approximately one hundred microns,and in particular for cutting “thin” or useful layers, having athickness on the order of one micron.

It should be noted that the term “cutting” when used herein meansdividing a single item or assembly into two distinct parts such that theparts are not joined again. As discussed below, such cutting within thescope of the invention is conducted on a weakened zone.

Devices and methods are used to form layers (thin or not), which may betransferred from the source substrate to a “target” substrate. Thesubstrates generally come in the form of disks generally referred to inthe field as “wafers”. The wafers may be made of a semi-conductormaterial such as silicon.

A person skilled in the art knows how to form a weakened zone inside awafer along a plane that is parallel to the main faces of the wafer. Forexample, the weakened zone may be produced by implanting ions throughthe surface of the wafer. The ions create a weakened layer in the volumeof the wafer that delimits a lower region (which corresponds within thescope of this text to the source substrate) and an upper region adjacentto the ion source (which corresponds to the layer to be cut). An exampleof such a method used to produce thin layers is found in U.S. Pat. No.5,374,564.

It is also possible to produce the weakened zone by other known means,for example, by constructing an intermediate region of porous materialbetween two regions of dense material. An embedded oxide layer could beformed in a substrate (e.g. an Silicon On Insulator (SOI) typesubstrate) or by adhering two layers together, wherein the adhesion zonecorresponds to the weakened zone.

It should also be noted that it is possible to process SOA (Silicon OnAnything) type substrates or even AOA (Anything On Anything) typesubstrates in this manner. Thus, the cutting of such substrates fallswithin the scope of the invention.

To implement cutting along the weakened zone and to thus divide thesource substrate and the layer of material into two distinct parts, itis possible to use a manual operator. However, using a manual operatorlimits the layer production output. In addition, such operations may notbe reproducible. Automatic cutting devices and methods aiming to do awaywith the abovementioned drawbacks are known. An example of such a deviceand method is disclosed in U.S. Pat. No. 6,418,999. The device accordingto this patent uses a water jet to impact a slice of a wafer which isheld on its two main faces, wherein the water jet engages a weakenedzone and divides the wafer into two parts. This device includes holdingmeans associated with the two respective faces of the wafer, and theholding means enables a certain predetermined separation to occurbetween the two parts of the wafer during cutting.

It is important to manage the separation between the two parts of thewafer located on either side of the weakened zone with precision,particularly when these two parts are made of different materials. Forexample, when cutting an assembly including a layer of silicon attachedto an SiC substrate via a weakened zone, the silicon layer undergoessignificant deformation (the SiC substrate being considerably more rigidand undergoing considerably less deformation), which may cause damage tothe silicon layer.

The device disclosed in U.S. Pat. No. 6,418,999 attempts to provide asolution to accompany separation and/or deformation of the two parts ofthe wafer in the desired manner. However, one restriction associatedwith this device is that it includes only passive means to enable aspecific separation and/or a specific deformation. The passive meanscorrespond to specific configurations of the holding means, wherein thesurface may include cavities of given geometries to enable a specificspacing between the parts of the wafer. It is also possible, accordingto this document, to give the surface of the holding means a generallyconvex shape, or to provide a layer of elastic material on the surfaceof the holding means which contacts the wafer. But such passivesolutions cannot be used to accompany the separation or spacing apartand/or deformation of the parts of the wafer because there is no actualcontrol (i.e. control in active mode) carried out by the devicedisclosed in U.S. Pat. No. 6,418,999. In addition, it should be notedthat the holding means must also rotate the wafer so that the entireperiphery of the wafer is engaged by a water jet, which complicates thedesign and operation of the device.

SUMMARY OF THE INVENTION

Presented is an automatic cutting device for cutting an assembly. Theassembly includes a material having a weakened zone therein that definesa useful layer and being attached to a source substrate. The cuttingdevice includes a cutting mechanism and a holding and positioningmechanism operatively associated with the cutting mechanism. The holdingand positioning mechanism positions the material so that the cuttingmechanism detaches the layer from the source substrate along theweakened zone. The cutting device also includes a control mechanism foradjusting at least two different portions of the assembly duringdetachment of the layer to facilitate a more precise detachment.

In an advantageous embodiment, the cutting mechanism includes a bladefor contacting the assembly. The cutting mechanism may also includemeans for generating a pressurized fluid jet. In a preferred embodiment,the cutting mechanism includes two blades. In a beneficialimplementation, the cutting mechanism includes at least one blade havinga leading edge with a crescent-shaped profile for engaging a peripheryof the assembly.

In an advantageous implementation, the holding and positioning mechanismis moveable to induce strains in the assembly to facilitate cutting. Inaddition, the holding and positioning mechanism could include at leasttwo grippers associated with at least two different portions of theassembly. In a beneficial implementation, the holding and positioningmechanism is controllable in a direction perpendicular to a cuttingplane. The holding and positioning mechanism may also be controllable ina direction parallel to a cutting plane.

An advantageous implementation of the invention includes-a sensorcapable of acquiring a representative data item corresponding to theprogress of a cutting operation. A control loop may also be used forutilizing the representative data to control the movements of theholding and positioning mechanism. In a preferred embodiment, the sensormeans comprises light-emitting diodes arranged on either side of theassembly for generating data concerning the progress of the detachmentof the layer from the source substrate.

Another aspect according to the invention concerns a method forautomatically cutting an assembly that includes a material having aweakened zone therein that defines a useful layer, and being attached toa source substrate. The method includes positioning the assembly with aholding and positioning mechanism, and cutting the assembly with acutting mechanism while concurrently controlling the movement of theholding and positioning mechanism such that the layer is detached fromthe source substrate along the weakened zone. At least two differentportions of the assembly are adjusted during detachment of the layer tofacilitate a more precise detachment.

In a preferred implementation, the movement of the holding andpositioning mechanism is controlled in conjunction with contacting theassembly with the cutting means. Advantageously, the method includesacquiring at least one data item representative of the progression ofthe cutting operation, and controlling the movement of the holding andpositioning mechanism based on the data item. In a preferred embodiment,the method includes controlling the movement of the holding andpositioning mechanism in a direction parallel to a cutting plane of theassembly. In addition, the method beneficially includes controlling themovement of the holding and positioning mechanism in a directionperpendicular to a cutting plane of the assembly.

The invention thus makes it possible to carry out entirely automatedcutting operations.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, purposes and advantages of the invention will becomeclear after reading the following detailed description with reference tothe attached drawings, in which:

FIG. 1 is a simplified schematic side view of a cutting device accordingto the invention; and

FIG. 2 is a simplified schematic top view of the device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a cutting device 10 and a wafer 20 forming acutting assembly are schematically represented. It should be noted that,while in the simplified schematic representations in the figures thewafer 20 is represented with an apparently significant thickness, inreality the wafer may be extremely thin. Typically, the wafer may have athickness of a few millimeters, and a diameter which may be on the orderof 20 to 30 centimeters (these values are exemplary only, and are notmeant to limit the invention in any manner).

The wafer 20 consists of two parts 20 a and 20 b having a generally diskshape. An intermediate region 20 c extends between the two parts 20 aand 20 b and includes a weakened zone 200 c. The weakened zone 200 cgenerally extends along a plane that is parallel with the main faces ofthe wafer. The weakened zone may, as mentioned in the backgroundsection, have been produced by implantation of ions, but also may beformed by any other means known in the art. It should be noted that thetwo parts 20 a and 20 b may be made of the same material (particularlyin the case where the weakened zone 200 c is formed by implantation ofatomic species), or may be made of different materials. By convention,the term “source substrate” refers to the bottom part 20 b of the wafer,and the term “cutting layer” refers to the top part 20 a.

As shown in FIG. 1, the edges of the two parts 20 a and 20 b may berounded or chamfered, which is standard practice particularly for layersof semiconductor material. In this case, the two parts 20 a and 20 bdefine an annular chamfer 21 c on the intermediate region 20 c. However,it is also possible for the edges of the parts 20 a and 20 b to all haveanother given geometry.

The device 10 includes at least one blade to contact or engage the wafer30 at its weakened zone 200 c. In the specific example represented inFIGS. 1 and 2, the device 10 comprises two blades 101 and 102 arrangedin the plane of the weakened zone 200 c (referred to hereinafter as the“cutting plane”), and a holding means. The two blades are diametricallyopposed to each other at either end of the wafer so as to engage it onopposite sides of its periphery. However, it is also possible to producethe device 10 with only one blade, because it is possible to simplyremove one of the two blades or to replace a blade with a fixed wedge tohelp hold the wafer in position during cutting (this holding functionbeing conducted elsewhere as described below).

In an implementation of the invention, the holding means are in the formof two grippers 100 a and 100 b that are associated with oppositeexternal faces of the respective parts 20 a and 20 b of the wafer 20.The grippers 100 a and 100 b each comprise gripping means for grippingone of the faces of the wafer. The gripping means may, for example,comprise suction cups and/or surface cavities on the gripper which arefor use in contacting the wafer. In an implementation, it is possible toevacuate the cavities to attach the gripper and a surface of the wafer.The gripping means may also be produced in any form known in the art,allowing them to grip a wafer surface by providing a sufficient level ofcohesion between the gripper and its associated wafer part so as torigidly hold the assembly during the entire cutting operation (includingduring the engagement of the blade which is described in detail below).Each of the two grippers 100 a and 100 b is also mounted on respectivemovement means, capable of moving an associated gripper in the cuttingplane and in a “vertical” direction that is perpendicular to the cuttingplane. The gripper movement means are not represented in the figures forsimplification and clarity purposes. It should be noted, however, thatthe movement means are capable of controlling the movement of eachgripper independently of the other gripper.

In an implementation, control means are associated with each blade ofthe device to control the movement of the blade in the cutting plane, asthe blade is moved from the outside of the wafer towards it center. Itshould be noted that while the blades have been represented in thefigures with a significant apparent thickness, as mentioned aboveconcerning the wafer itself, the blades are very thin in reality (on theorder of one millimeter). The blade engages the periphery of the waferat the weakened zone without necessarily penetrating to the center ofthe wafer.

As shown in the top view of FIG. 2, in an implementation the blades havea crescent-shaped leading edge wherein the concavity corresponds to thecurvature of the periphery of the wafer, so as to engage a significantpart of the periphery. It is also possible to provide for a main bladeto contact the wafer to initialize the cutting operation by generating adetachment front which is propagated between the two parts 20 a and 20b. Two other blades could then be used to engage the wafer, taking overfrom the main blade. These two blades could be positioned symmetricallyon either side of the wafer with respect to the direction of engagementof the first blade.

In any case, irrespective of the number of blades used in an embodimentof the device and their particular movement kinematics, the movement ofthe grippers is also controlled in conjunction with the engagement ofthe blades into the wafer. It is the specific combination of the meansmentioned above (blade(s) and grippers) which makes it possible to cutthe wafer under optimal conditions. More specifically, it is thecombination of the action of each blade of the device -and the gripperswhich act on the two external faces of the wafer, which makes itpossible to carry out effective cutting of the wafer. In particular, themovement of each blade is controlled so that a blade engages the waferat its weakened zone 200 c, in conjunction with controlling the movementof each gripper according to predetermined kinematics. It is noted thatthe it is possible for the movement kinematics of the two grippers to bedifferent while being synchronized with each other.

Therefore, the grippers carry out the following functions, inconjunction with the engagement of wafer by the blade(s). First, thegrippers hold their associated wafer part in the cutting plane, suchthat the position of the wafer is controlled in the cutting plane duringengagement of the blade(s). This control of the position of the parts ofthe wafer may, for example, be conducted by immobilizing the parts ofthe wafer during a specific cutting phase, particularly during theinitial engagement of the wafer by the blade. The grippers thus formholding means for the wafer, which enable the blades to engage the waferunder optimal conditions. Second, the grippers are moved in a controlledmanner in the cutting plane, and/or in the vertical direction. Theprimary effect of controlling the movement of the parts of the wafer inthe vertical direction is to accompany, in a controlled and activemanner, the deformation of the parts of the wafer that results from theengagement of the blade(s) and the propagation of a detachment frontbetween the material layer and the source substrate. It is possible toobserve or monitor the propagation of the detachment front and controlthe movement of the grippers in a direction away from the wafer surfaces(in a vertical direction) as the detachment front progresses by using asuitable control loop.

It should be noted that, with a view to a fully automated device withhigh reliability and durability qualities, a preferred solution consistsof controlling the movement of the grippers (both vertically and in thecutting plane as described below) not by observing the propagation of adetachment front, but by monitoring the spacing between the two parts ofthe wafer. A description of a simple means used to effectively monitorthe separation is given below. In this case, the control loop which isused to control the movement of each gripper is controlled by theseparation or spacing apart observations from such means. In this way,active control is conducted concerning the separation and/or deformationof the parts of the wafer being cut. This arrangement is advantageous,particularly in contrast to the means disclosed by U.S. Pat. No.6,418,999 which are purely passive and are subjected to the deformationof the parts of the wafer without actively influencing the deformation.

More specifically, the controlled movement of the parts of the waferalong the vertical direction may be used to correct for the deformationand/or spacing of the parts of the wafer during cutting. For example, ifthe deformation and/or spacing monitored (by a specially adapted camera,or for example, by any optical system and a specific development isdiscussed below) does not correspond to desired conditions (the observedvalues of deformation of and/or spacing between wafer parts are too low,or are too high, or are not progressing in the desired manner) thencorrective movements are conducted. Each wafer part 20 a or 20 b couldbe moved to obtain such corrections, and each part may be movedindependently from the other part. Also, the movements of the waferparts may not necessarily be symmetric (particularly if the two partsare made of different materials that have different mechanicalcharacteristics). In this manner, it may be possible to keep one of thegrippers immobile because of the characteristics of the wafer(particularly due to the nature of the materials forming the two partsof the wafer), while controlling only the movement of the other gripper.

It should be noted that, if a required control means is designed tocontrol the movements of each gripper, the surface of the grippers whichcontact an associated wafer face may be of any desired shape, such as ashape that is suitable for favoring a particular type of deformation(for example, a convex shape, a gripper surface comprising cavities orchannels, and the like).

In addition to the control of the deformation and/or spacing between theparts of the wafer during cutting, the movements of the grippers in thevertical direction may also be controlled to induce a tensile strain inthe wafer (along the arrows Ta and Tb shown in FIG. 1), so as to furtherfavor cutting. It is also noted that the gripping means associated witheach gripper guarantees a rigid connection between each gripper and itsassociated wafer part, such that each gripper subjects each wafer partto tensile strain. It is also possible, in combination with the abovearrangements, to control movement of the grippers in the cutting plane.For example, the grippers could be moved along opposite and possiblyalternative trajectories, to induce a shearing strain between the twoparts of the wafer. This also would favor cutting. This shearing effectis represented in FIG. 1, shown by the arrows Ca and Cb which representthe opposite strains applied to both respective parts of the wafer,parallel to the cutting plane, but in opposite directions.

The cohesive force between each gripper and its associated wafer part issufficient for the gripper to remain completely attached to itsassociated wafer part during various movements. In this manner, theinvention offers a completely original combination of cutting means, andholding means capable of being moved in a controlled manner. Thisarrangement makes it possible to combine the advantages of theengagement of an assembly to be cut by a blade, which acts as a “wedge”inserted between the two parts of the wafer. The arrangement thus favorsthe generation of a detachment front under the effect of the gripperswhich induce strains in the wafer.

It should be noted that the blade(s) of the device may be replaced byanother type of cutting means, so long as the effect is combined withthat of the holding means represented by the grippers. The cutting meansmay thus be means enabling the generation of a pressurized fluid jet,which is targeted at the weakened zone of the wafer. In addition, it ispossible to provide a cutting means associated with the grippers thatcombines at least one blade and means used to generate such apressurized fluid jet. Therefore, at least one blade of the device mayinclude an internal pressurized fluid supply channel, wherein thechannel opens onto the tip of the leading edge of the blade to enablethe projection of the fluid on the weakened zone of the wafer incombination with the blade engagement.

All the arrangements mentioned above with respect to the control of theposition and movement of the grippers, and therefore the associatedwafer parts, will preferentially be implemented in combination with asystem to monitor the deformation and/or spacing apart of the parts ofthe wafer. More specifically, in order to provide a reliable and robustautomatic device, an advantageous solution is to select direct viewingmeans to monitor the spacing as the parts of the wafer separate duringcutting. It will thus be possible to arrange a series of light-emittingdiodes in the cutting plane on either side of the wafer, with respect tothe general direction of engagement of the blade(s) of the device(therefore with respect to the general direction of propagation of thedetachment front). The series of light-emitting diodes extend along thegeneral direction of engagement of the blades (in the direction of thearrows F1 of FIG. 2). In an implementation, the diodes are arranged inpairs on either side of the general direction of engagement of theblade(s), each diode from a given pair being opposite the other. A diodefrom each pair thus emits a light beam towards another diode, whichreceives the beam in the absence of obstacles between the two diodes.Thus, when the parts of the wafer, normally inserted between the twodiodes from each pair, are sufficiently separated (due to cutting), thebeam emitted by the emitting diode is received by the receiving diode.

By arranging the pair of diodes in the general direction of engagementof the blade(s) of the device, and by connecting each receiving diode toa central monitoring unit equipped with a processor, it is possible tomonitor the progression of the separation or spacing apart of the partsof the wafer, and to then control the movement of the grippersaccordingly.

It should be noted that it is possible to adapt the respectivekinematics governing the effect of the cutting means and of thegrippers, to adapt the mechanical strains applied between the two partsof the wafer in an optimal fashion, according to the characteristics ofthe wafer (for example, according to the nature of the materials formingthe two parts of the wafer, and the like).

As a general rule, it is thus important for the controlled movements ofthe grippers to be carried out in conjunction with, or in combinationwith, the engagement of the wafer by the cutting means. The term “inconjunction” generally refers to the combination of the effect of bothtypes of means. Thus, in an alternative embodiment of the invention, itis possible to control the contact of the cutting means (blade(s) orother cutting means) with the weakened zone of the wafer, after whichthe grippers are initialized to make use of the initial separation orspacing apart between the parts of the wafer caused by the “wedge”effect of the cutting means. However, in another alternative embodiment,it is possible to first cause separation of both parts of the wafer byapplying opposite tensile forces by movement of the grippers on bothrespective parts, before initializing the cutting means.

1. An automatic cutting device for cutting an assembly that includes amaterial having a weakened zone therein that defines a useful layer andbeing attached to a source substrate, comprising: a cutting mechanism; aholding and positioning mechanism operatively associated with thecutting mechanism to position the material so that the cutting mechanismdetaches the layer from the source substrate along the weakened zone;and a control mechanism for adjusting at least two different portions ofthe assembly during detachment of the layer to facilitate a more precisedetachment.
 2. The device of claim 1 wherein the cutting mechanismcomprises a blade for contacting the assembly.
 3. The device of claim 1,wherein the cutting mechanism comprises means for generating apressurized fluid jet.
 4. The device of claim 1, wherein the holding andpositioning mechanism is moveable to induce strains in the assembly tofacilitate cutting.
 5. The device of claim 1, wherein the holding andpositioning mechanism comprises at least two grippers associated withthe at least two different portions of the assembly.
 6. The device ofclaim 1, wherein the holding and positioning mechanism is controllablein a direction perpendicular to a cutting plane.
 7. The device of claim1, wherein the holding and positioning mechanism is controllable in adirection parallel to a cutting plane.
 8. The device of claim 1, furthercomprising a sensor capable of acquiring a representative data itemcorresponding to the progress of a cutting operation.
 9. The device ofclaim 8, further comprising a control loop for utilizing therepresentative data to control the movements of the holding andpositioning mechanism.
 10. The device of claim 8, wherein the sensorcomprises light-emitting diodes arranged on either side of the assemblyfor generating data concerning the progress of the detachment of thelayer from the source substrate.
 11. The device of claim 1, wherein thecutting mechanism comprises two blades.
 12. The device of claim 1,wherein the cutting mechanism includes at least one blade having aleading edge with a crescent-shaped profile for engaging a periphery ofthe assembly.
 13. A method for automatically cutting an assembly thatincludes a material having a weakened zone therein that defines a usefullayer and being attached to a source substrate, comprising: positioningthe assembly with a holding and positioning mechanism; and cutting theassembly with a cutting mechanism while concurrently controlling themovement of the holding and positioning mechanism such that the layer isdetached from the source substrate along the weakened zone, wherein atleast two different portions of the assembly are adjusted duringdetachment of the layer to facilitate a more precise detachment.
 14. Themethod of claim 13, wherein the movement of the holding and positioningmechanism is controlled in conjunction with contacting the assembly withthe cutting mechanism.
 15. The method of the claim 13, furthercomprising acquiring at least one data item representative of theprogress of cutting, and controlling the movement of the holding andpositioning mechanism based on the data item.
 16. The method of claim13, which further comprises controlling the movement of the holding andpositioning mechanism in a direction parallel to a cutting plane of theassembly.
 17. The method of claim 13, which further comprisescontrolling the movement of the holding and positioning mechanism in adirection perpendicular to a cutting plane of the assembly.